Vehicles today commonly employ multiple localized control systems each comprising a plurality of different sensors and actuators. These localized control systems work individually or in tandem to control vehicle behavior. For example, the vehicle propulsion system and braking system can be operated in tandem to effect sophisticated control over the vehicle handling in the face of diverse conditions. Because these localized control systems can operate independently or in combination there may be many ways to accomplish the same end result. For this reason it can often be unclear which control has overriding responsibility for vehicle behavior at any point in time.
The traditional solution to such ambiguity, which has evolved over time, is simply to use a collection of design rules for automotive engineers to follow. For example, in the case of vehicle yaw control, both the steering system and the braking system can affect yaw and yaw change in a vehicle. Thus a standard has evolved that places the braking system in the primary role of yaw master, with the steering system taking a subservient role.
There is nothing inherently wrong with employing standards that place one control system in a superior role with respect to other systems that are also responsible for the controlled vehicle behavior. However, vehicles are becoming more complicated and the fixed rules of the past may no longer be optimal or appropriate. For example, hybrid vehicles have recently become popular. In such vehicles there are multiple sources of propulsion: the wheels may be driven by both internal combustion engine and electric motor. In some cases, each wheel may be independently driven by its own dedicated motor. Thus the torque delivered to the vehicle at any given point in time can be a complex blend produced by both internal combustion engine and electric motor or motors. The rigid standards of the past are often ill-equipped to handle these situations.
To make matters even more challenging, the ambiguity as to which system is in control can change dynamically. Depending on driving conditions, the optimal allocation of control may switch from one propulsion system to another. Thus, it may not be appropriate to simply establish by design rule that one system should always takes precedence over the other, because the reasons for selecting one system over the other may change under different driving conditions. Thus, a preferred solution would be to have flexible control to allow intelligent decisions to be made with respect to the control hierarchy, based on actual vehicle operating conditions.